Response of changes in soil nutrients to soil erosion on a purple soil of cultivated sloping land

Severe soil erosion of cultivated sloping land in hilly areas of Sichuan, China, has resulted in deterioration of soil quality, and therefore has an adverse impact on crop production. A hillslope of 110 m in length was selected with a slope steepness of 10.12% where the soils were classified as Regosols. Soil samples for determining ¹³⁷Cs, soil organic matter (SOM), total N, P, K, available N, P, K and particle size fraction were collected at 10 m intervals along a transect of the hillslope. Loss of soil nutrients owing to soil erosion was studied by using ¹³⁷Cs technique, and the relationships between ¹³⁷Cs-derived soil redistribution rates and soil nutrients were established over the cultivated sloping land in hilly areas of Sichuan, China (30o26′N, 104o28′E). The values of SOM, total N, available N, P, K and the soil particle fractions of size < 0.002 mm were smaller at upper and middle slope positions where ¹³⁷Cs inventories were lower (i.e., soil erosion rates were higher) than at downslope positions where ¹³⁷Cs inventories were higher (i.e., soil erosion rates were lower). The lowest ¹³⁷Cs inventories were found at the hilltop, showing that besides erosion owing to water flow, tillage also contributed to soil losses, and intensive tillage was mostly responsible for severe erosion at upper slope positions. There were significant differences in SOM, total N, available N, P, K and the soil particle fractions of size < 0.002 mm between different slope segments, and these properties were significantly correlated with slope length. These soil properties were also significantly correlated with ¹³⁷Cs inventories, indicating that both ¹³⁷Cs and nutrient concentrations varied with topographical changes. The variation in soil properties was strongly influenced by erosion-induced soil redistribution, and therefore ¹³⁷Cs inventories mirroring soil redistribution rates would be considered as an integrated indicator of soil quality.     

黑土坡耕地有机碳及其组分累积-损耗格局对耕作侵蚀与水蚀的响应

耕作与水蚀是黑土区坡耕地碳库退化的主导因素,为进一步探究土壤有机碳(SOC)及其组分对不同侵蚀驱动力(耕作、水力)的响应格局,基于该区耕作侵蚀与水蚀模型,在定量表达耕作侵蚀-沉积量与水蚀量的基础上,利用地统计学的方法,分析了东北黑土区典型漫岗地形坡面尺度SOC及其3种组分的空间分布特征.结果表明: 耕作侵蚀与沉积速率分别表现为坡上>坡下>坡中>坡脚和坡脚>坡下>坡中>坡上;水蚀速率表现为坡下>坡脚>坡中>坡上;坡下陡坡位置耕作侵蚀与水蚀协同引起严重的土壤流失.虽然耕作侵蚀速率(0.02～7.02 t·hm^-2·a^-1)远小于水蚀速率(5.96～101.17 t·hm^-2·a^-1),但耕作侵蚀在全坡面范围均可对SOC产生不同程度的影响,而水蚀则主要在坡下径流汇集区显著影响SOC的累积-损耗.受水蚀与耕作侵蚀-沉积作用影响,SOC、颗粒有机碳、水溶性有机碳在侵蚀点含量低于沉积点,而微生物生物量碳变化趋势相反;耕作侵蚀通过影响颗粒有机碳参与SOC的积累-损耗过程.     

137Cs和210Pbex示踪黑土区坡耕地

通过在野外28.5 hm²的坡耕地上采集土壤样品,定量评价了利用¹³⁷Cs和²¹⁰Pb_ex研究土壤有机碳(SOC)动态的潜力,以探讨东北黑土区土壤侵蚀对土壤有机碳的影响.结果表明:农耕地土壤¹³⁷Cs、²¹⁰Pb_ex和SOC在平面和垂直深度上均具有相似的分布特征.在平面上,尽管受土壤侵蚀沉积的影响,¹³⁷Cs、²¹⁰Pb_ex面积活度及SOC储量变异很大,但它们具有相同的变化趋势.在垂直断面上,侵蚀区¹³⁷Cs、²¹⁰Pb_ex和SOC在0～25 cm耕层内分布均匀,25 cm以下放射性活度减小,SOC含量也相应下降;沉积区0～100 cm深度上¹³⁷Cs和²¹⁰Pb_ex呈现先增加后减小的分布规律,SOC也具有类似的变化特征.农耕地SOC与¹³⁷Cs、²¹⁰Pb_ex呈显著线性相关,表明它们在黑土区农耕地上具有相似的物理运移特征,¹³⁷Cs和²¹⁰Pb_ex可直接用来定量评价黑土侵蚀下SOC的时空分布特点.     

桂西北喀斯特坡地土壤137Cs的剖面分布特征及其指示意义

分析了137Cs及土壤有机碳(SOC)在桂西北典型峰丛坡地及岩溶裂隙中的剖面分布特征,探讨了137Cs方法在喀斯特坡地的适用性及其指示的坡面土壤侵蚀特征.结果表明:所有剖面137Cs与SOC均显著相关,两者可能有相同的流失途径;次生林坡地137Cs主体分布深度在24 cm以内,中上及中坡剖面随深度呈指数递减分布,地表无侵蚀或侵蚀轻微,坡脚剖面呈较严重侵蚀形态;坡耕地剖面137Cs在耕层内均匀分布,中上坡及中坡主体分布深度在15 cm左右,面积活度远低于背景值,土壤侵蚀剧烈,坡脚分布深度至45 cm,呈堆积形态;次生林坡脚剖面、耕地中上坡剖面及所有裂隙剖面,137Cs在主体分布深度以下有断续极微量的分布,指示了喀斯特坡地土壤颗粒有随降雨沿地表负地形向地下流失的趋势,但流失量轻微.     

Modelling the impact of agricultural management on soil carbon stocks at the regional scale: the role of lateral fluxes

Agricultural management has received increased attention over the last decades due to its central role in carbon (C) sequestration and greenhouse gas mitigation. Yet, regardless of the large body of literature on the effects of soil erosion by tillage and water on soil organic carbon (SOC) stocks in agricultural landscapes, the significance of soil redistribution for the overall C budget and the C sequestration potential of land management options remains poorly quantified. In this study, we explore the role of lateral SOC fluxes in regional scale modelling of SOC stocks under three different agricultural management practices in central Belgium: conventional tillage (CT), reduced tillage (RT) and reduced tillage with additional carbon input (RT+i). We assessed each management scenario twice: using a conventional approach that did not account for lateral fluxes and an alternative approach that included soil erosion‐induced lateral SOC fluxes. The results show that accounting for lateral fluxes increased C sequestration rates by 2.7, 2.5 and 1.5 g C m^?2 yr^?1 for CT, RT and RT+i, respectively, relative to the conventional approach. Soil redistribution also led to a reduction of SOC concentration in the plough layer and increased the spatial variability of SOC stocks, suggesting that C sequestration studies relying on changes in the plough layer may underestimate the soil's C sequestration potential due to the effects of soil erosion. Additionally, lateral C export from cropland was in the same of order of magnitude as C sequestration; hence, the fate of C exported from cropland into other land uses is crucial to determine the ultimate impact of management and erosion on the landscape C balance. Consequently, soil management strategies targeting C sequestration will be most effective when accompanied by measures that reduce soil erosion given that erosion loss can balance potential C uptake, particularly in sloping areas.     

The dynamics of soil redistribution and the implications for soil organic carbon accounting in agricultural south‐eastern Australia

Anthropogenically induced change in soil redistribution plays an important role in the soil organic carbon (SOC) budget. Uncertainty of its impact is large because of the dearth of recent soil redistribution estimates concomitant with changing land use and management practices. An Australian national survey used the artificial radionuclide caesium‐137 (¹³⁷Cs) to estimate net (1950s–1990) soil redistribution. South‐eastern Australia showed a median net soil loss of 9.7 t ha^?1 yr^?1. We resurveyed the region using the same ¹³⁷Cs technique and found a median net (1990–2010) soil gain of 3.9 t ha^?1 yr^?1 with an interquartile range from ?1.6 t ha^?1 yr^?1 to +10.7 t ha^?1 yr^?1. Despite this variation, soil erosion across the region has declined as a likely consequence of the widespread adoption of soil conservation measures over the last ca 30 years. The implication of omitted soil redistribution dynamics in SOC accounting is to increase uncertainty and diminish its accuracy.     

黄土区耕作侵蚀及其对总土壤侵蚀贡献的空间格局

耕作能直接造成大量的土壤向坡下运动 ,却在以往土壤侵蚀研究中被忽视。为了定量评价耕作侵蚀以及在坡耕地土壤侵蚀中的重要性 ,通过耕作侵蚀示踪试验及铯 - 1 37示踪的方法对黄土区耕作侵蚀及其对总土壤侵蚀贡献的空间格局进行了研究 ,取得了如下结果 :( 1 )一次耕作造成的单宽土壤搬运量为 2 3.60～ 45 .68kg/m,并从坡地上部和下部向中部逐渐变大 ;( 2 )耕作侵蚀强度主要集中在 70 0～ 2 0 0 0 t/km2 和- 1 2 0 0～ - 2 0 0 0 t/km2 之间 ,分别发生在坡地凸型和凹型部位 ;( 3)总土壤侵蚀强度主要集中在 2 60 0～890 0 t/( km2· a)和 - 2 75 0～ - 3390 t/( km2· a)之间 ,分别发生在坡地凸型部位与凹型部位的上部及坡地凹型部位的下部 ;( 4 )耕作侵蚀占总土壤侵蚀的百分比 ,主要集中在 1 0 %～ 2 8%、- 2 7%～ - 398%和 36%～ 5 4 %之间 ,从坡顶向坡底 ,依次分布在两种侵蚀皆呈侵蚀的部位、耕作侵蚀呈沉积而总土壤侵蚀呈侵蚀的部位及两种侵蚀皆呈沉积的部位。结果表明 ,耕作侵蚀是黄土区坡耕地的一种重要的土壤侵蚀 ,是总土壤侵蚀的重要组成部分 ,水土保持工作中应充分考虑耕作侵蚀及其对总土壤侵蚀贡献的空间格局。     

桂西北喀斯特坡地土壤137Cs的剖面分布特征及其指示意义

分析了¹³⁷Cs及土壤有机碳（SOC）在桂西北典型峰丛坡地及岩溶裂隙中的剖面分布特征,探讨了¹³⁷Cs方法在喀斯特坡地的适用性及其指示的坡面土壤侵蚀特征.结果表明：所有剖面¹³⁷Cs与SOC均显著相关,两者可能有相同的流失途径;次生林坡地¹³⁷Cs主体分布深度在24 cm以内,中上及中坡剖面随深度呈指数递减分布,地表无侵蚀或侵蚀轻微,坡脚剖面呈较严重侵蚀形态;坡耕地剖面¹³⁷Cs在耕层内均匀分布,中上坡及中坡主体分布深度在15 cm左右,面积活度远低于背景值,土壤侵蚀剧烈,坡脚分布深度至45 cm,呈堆积形态;次生林坡脚剖面、耕地中上坡剖面及所有裂隙剖面,¹³⁷Cs在主体分布深度以下有断续极微量的分布,指示了喀斯特坡地土壤颗粒有随降雨沿地表负地形向地下流失的趋势,但流失量轻微.     

水土流失治理措施对小流域土壤有机碳和全氮的影响

明确综合治理条件下小流域土壤有机碳(Soil organic carbon,SOC)和全氮(Total nitrogen,TN)的空间分布特征及其影响因素,对科学评价水土流失区土壤固碳潜力具有重要意义。以黄土高原丘陵沟壑区典型小流域(砖窑沟流域)为对象,基于流域内3种典型地貌类型(梁峁坡、沟坡、沟谷)和3种典型水土流失治理措施(水平梯田、林地和草地措施,坡耕地为对照),采集土壤样品737个,研究地貌类型和水土流失治理措施对小流域SOC和TN变化的影响。结果表明,同一地貌类型上,水平梯田、林地和草地措施的SOC和TN(0—10 cm土层)含量均显著高于坡耕地(P<0.1)。梁峁坡上,水平梯田、林地和草地措施条件下的SOC和TN含量较坡耕地依次提高了18%和24%、70%和59%、25%和21%;沟坡上,林地和草地措施的SOC和TN较坡耕地依次提高了76%和54%、25%和27%。同一治理措施在不同地貌类型间对0—10 cm土层SOC和TN的影响存在显著差异(P<0.1)。水平梯田条件下,沟谷的SOC和TN含量比峁坡提高了46%和43%;林地措施条件下,沟坡的SOC和TN含量比峁坡提高了18%和6%;草地措施条件下,沟坡的SOC和TN含量比峁坡提高了14%和18%。0—100 cm土层的SOC或TN在不同地貌类型或不同治理措施间的差异与土壤水分含量(Soil moisture,SM)的变化趋势基本一致,并且SOC或TN与SM呈指数关系y=aebx(y为SOC或TN,x为SM)。     

保护性耕作对农田碳、氮效应的影响研究进展

作物产量的高低主要取决于土壤肥力,如何保持并提高土壤肥力是确保我国粮食安全和农业可持续发展的重要任务,也是众多学者关注的焦点。土壤有机碳和氮素是评价土壤质量的重要指标,其动态平衡直接影响土壤肥力和作物产量。随着全球气候变化及环境污染问题的愈加突出,农田土壤固碳及提高氮效率成为各界科学家研究的热点。目前,保护性耕作已成为发展可持续农业的重要技术之一,对土壤固碳及氮素的利用具有很大的影响。深入了解保护性耕作对土壤有机碳固持与氮素利用效率提高的影响机制,对于正确评价土壤肥力有着重要意义。但由于气候、土壤及种植制度等条件不一致,关于保护性耕作对农田碳、氮效应结论不一。阐述了国际上保护性耕作对农田系统土壤有机碳含量变化及其分解排放(如CO₂和CH₄)、氮素变化及其矿化损失(如NH₃挥发、N₂O排放与氮淋失)和碳氮素相互关系(如C/N层化率)影响的研究进展,并分析了其影响因素和相关机理。尽管国内保护性耕作的研究已进行30 多年,但在土壤有机碳与氮素方面与国外相比依然有较大的差距。保护性耕作对土壤固碳与氮素利用的影响机制,碳素和氮素在土壤-植株-大气系统中的转移变化,及结合农事管理等综合评价其生态效应的研究很少。在此基础上,提出未来我国保护性耕作在土壤有机碳固定和氮素利用方面的重点研究方向:(1)在定位试验基础上进一步探讨保护性耕作对土壤有机碳及氮素利用的影响机制;(2)深入研究土壤有机碳和氮素的相互关系及其对土壤肥力的影响;(3)结合环境保护与土壤可持续管理对保护性耕作农田土壤固碳及氮素高效利用的系统评价研究;(4)加强保护性耕作对农田碳、氮效应的宏观研究,合理评价保护性耕措施下对农田碳、氮综合效应。     

137Cs示踪技术研究坡耕地黑土侵蚀和沉积特征

准确地测定研究区137Cs背景值,建立137Cs流失量与土壤再分布速率之间的定量模型是137Cs示踪技术的关键。通过野外选择参照样地和利用热核爆炸源137Cs背景值模型来确定研究区137Cs的背景值,在此基础上用体现耕作迁移的质量平衡模型估算黑土坡耕地不同地貌部位的土壤再分布速率,并对主要参数进行敏感性分析。结果表明(1)研究区实测的137Cs背景值为2376.81±108.46Bq/m2,模型预测值为2318.4Bq/m2,模型预测远离西北核试验基地的地区较为准确。(2)研究区中坡位(坡肩和坡背)137Cs含量最低,侵蚀最为强烈,平均侵蚀速率为33.56t/(hm2·a)和21.67t/(hm2·a);坡麓和坡足则明显表现沉积,平均沉积速率为-4.93t/(hm2·a)和-24.61t/(hm2·a)。(3)模型预测的侵蚀速率与耕层质量深度(d)、张驰深度(H)正相关,而与137Cs年沉降易被迁移的比例(γ)和颗粒校正因子(P)反相关。并且,模型对参数d、p的敏感性分别高于参数H和γ。     

基于SIMWE模型的典型水土保持措施侵蚀阻控路径分析——以通双小流域为例

针对东北黑土区长缓坡地形条件下坡面产汇流集中易加剧土壤侵蚀的问题,本研究基于GIS和SIMWE(SIMulated Water Erosion)模型,引入连通性指数和水深空间分布作为水文连通性与径流路径的衡量指标.通过量化不同典型水土保持措施对土壤入渗速率和地表曼宁糙率的影响,构建梯田数字高程模型(DEM)模拟表征地表...     

Land use effects on erosion and carbon storage of the Río Chimbo watershed, Ecuador

Background and aims

Soil carbon storage is an important component of global carbon cycling. Andean Andisols have high carbon content and are vulnerable to erosion because of agricultural intensification and deforestation. This study examines the effects of land use on erosion and soil carbon storage in the Río Chimbo watershed of Ecuador.

Methods

Soil carbon content, age, and erosion estimated from ¹³⁷Cs inventories was measured along an elevational transect under annual cropping, natural forest, páramo, pasture, and tree plantations.

Results

Land use, particularly annual cropping, affected ¹³⁷Cs levels in the upper soil layers, but did not have an impact on total carbon storage to a depth of 1 m. Relative erosion rates estimated from ¹³⁷Cs inventories at sites under annual cropping averaged 27 t ha^?1?y^?1 over the erosion rate of non-cultivated sites. A linear relationship was observed between soil carbon age (determined by ¹⁴C levels) and ¹³⁷Cs levels, where pasture sites had lower ¹³⁷Cs and older carbon compared to natural forest sites.

Conclusions

The effects of land use on soil loss in the Río Chimbo watershed suggest a loss and/or removal of soil carbon, particularly under annual cropping.     

Variation in soil carbon stocks and their determinants across a precipitation gradient in West Africa

We examine the influence of climate, soil properties and vegetation characteristics on soil organic carbon (SOC) along a transect of West African ecosystems sampled across a precipitation gradient on contrasting soil types stretching from Ghana (15°N) to Mali (7°N). Our findings derive from a total of 1108 soil cores sampled over 14 permanent plots. The observed pattern in SOC stocks reflects the very different climatic conditions and contrasting soil properties existing along the latitudinal transect. The combined effects of these factors strongly influence vegetation structure. SOC stocks in the first 2 m of soil ranged from 20 Mg C ha^?1 for a Sahelian savanna in Mali to over 120 Mg C ha^?1 for a transitional forest in Ghana. The degree of interdependence between soil bulk density (SBD) and soil properties is highlighted by the strong negative relationships observed between SBD and SOC (r² > 0.84). A simple predictive function capable of encompassing the effect of climate, soil properties and vegetation type on SOC stocks showed that available water and sand content taken together could explain 0.84 and 0.86 of the total variability in SOC stocks observed to 0.3 and 1.0 m depth respectively. Used in combination with a suitable climatic parameter, sand content is a good predictor of SOC stored in highly weathered dry tropical ecosystems with arguably less confounding effects than provided by clay content. There was an increased contribution of resistant SOC to the total SOC pool for lower rainfall soils, this likely being the result of more frequent fire events in the grassier savannas of the more arid regions. This work provides new insights into the mechanisms determining the distribution of carbon storage in tropical soils and should contribute significantly to the development of robust predictive models of biogeochemical cycling and vegetation dynamics in tropical regions.     

Losses of soil organic carbon under wind erosion in China

Soil organic carbon (SOC) storage generally represents the long‐term net balance of photosynthesis and total respiration in terrestrial ecosystems. However, soil erosion can affect SOC content by direct removal of soil and reduction of the surface soil depth; it also affects plant growth and soil biological activity, soil air CO₂ concentration, water regimes, soil temperature, soil respiration, carbon flux to the atmosphere, and carbon deposition in soil. In arid and semi‐arid region of northern China, wind erosion caused soil degradation and desert expansion. This paper estimated the SOC loss of the surface horizon at eroded regions based on soil property and wind erosion intensity data. The SOC loss in China because of wind erosion was about 75 Tg C yr^?1 in 1990s. The spatial pattern of SOC loss indicates that SOC loss of the surface horizon increases significantly with the increase of soil wind erosion intensity. The comparison of SOC loss and annual net primary productivity (NPP) of terrestrial ecosystem was discussed in wind erosion regions of China. We found that NPP is also low in the eroded regions and heavy SOC loss often occurs in regions where NPP is very small. However, there is potential to improve our study to resolve uncertainty on the soil organic matter oxidation and soil deposition processes in eroded and deposited sites.     

Effect of Erosion on Productivity in Subtropical Red Soil Hilly Region: A Multi-Scale Spatio-Temporal Study by Simulated Rainfall

The effects of water erosion (including long-term historical erosion and single erosion event) on soil properties and productivity in different farming systems were investigated. A typical sloping cropland with homogeneous soil properties was designed in 2009 and then protected from other external disturbances except natural water erosion. In 2012, this cropland was divided in three equally sized blocks. Three treatments were performed on these blocks with different simulated rainfall intensities and farming methods: (1) high rainfall intensity (1.5 - 1.7 mm min⁻¹), no-tillage operation; (2) low rainfall intensity (0.5 - 0.7 mm min⁻¹), no-tillage operation; and (3) low rainfall intensity, tillage operation. All of the blocks were divided in five equally sized subplots along the slope to characterize the three-year effects of historical erosion quantitatively. Redundancy analysis showed that the effects of long-term historical erosion significantly caused most of the variations in soil productivity in no-tillage and low rainfall erosion intensity systems. The intensities of the simulated rainfall did not exhibit significant effects on soil productivity in no-tillage systems. By contrast, different farming operations induced a statistical difference in soil productivity at the same single erosion intensity. Soil organic carbon (SOC) was the major limiting variable that influenced soil productivity. Most explanations of long-term historical erosion for the variation in soil productivity arose from its sharing with SOC. SOC, total nitrogen, and total phosphorus were found as the regressors of soil productivity because of tillage operation. In general, this study provided strong evidence that single erosion event could also impose significant constraints on soil productivity by integrating with tillage operation, although single erosion is not the dominant effect relative to the long-term historical erosion. Our study demonstrated that an effective management of organic carbon pool should be the preferred option to maintain soil productivity in subtropical red soil hilly region.     

Uncertainty in soil carbon accounting due to unrecognized soil erosion

The movement of soil organic carbon (SOC) during erosion and deposition events represents a major perturbation to the terrestrial carbon cycle. Despite the recognized impact soil redistribution can have on the carbon cycle, few major carbon accounting models currently allow for soil mass flux. Here, we modified a commonly used SOC model to include a soil redistribution term and then applied it to scenarios which explore the implications of unrecognized erosion and deposition for SOC accounting. We show that models that assume a static landscape may be calibrated incorrectly as erosion of SOC is hidden within the decay constants. This implicit inclusion of erosion then limits the predictive capacity of these models when applied to sites with different soil redistribution histories. Decay constants were found to be 15–50% slower when an erosion rate of 15 t soil ha^?1 yr^?1 was explicitly included in the SOC model calibration. Static models cannot account for SOC change resulting from agricultural management practices focused on reducing erosion rates. Without accounting for soil redistribution, a soil sampling scheme which uses a fixed depth to support model development can create large errors in actual and relative changes in SOC stocks. When modest levels of erosion were ignored, the combined uncertainty in carbon sequestration rates was 0.3–1.0 t CO₂ ha^?1 yr^?1. This range is similar to expected sequestration rates for many management options aimed at increasing SOC levels. It is evident from these analyses that explicit recognition of soil redistribution is critical to the success of a carbon monitoring or trading scheme which seeks to credit agricultural activities.     

东北黑土区坡耕地表层土壤颗粒有机碳和团聚体结合碳的空间分布

北黑土区典型漫岗坡耕地为研究对象,测定不同侵蚀程度地形部位表层土壤不同粒级有机碳、水稳性团聚体及其结合碳含量,探讨土壤侵蚀和沉积作用对表层土壤有机碳（SOC）损失、迁移和累积的影响.研究结果表明：与侵蚀微弱的坡顶相比,严重侵蚀的坡肩部位表层土壤水稳性大团聚体、矿质结合碳（IOC）和团聚体结合碳含量分别减少23﹪、17.5﹪和8.7﹪,而土壤颗粒有机碳（POC）含量无明显差异.长期处于沉积状态的坡脚部位,表层土壤大团聚体、POC和大团聚体结合碳含量分别较坡顶低56.1﹪、47.9﹪和67﹪;而IOC和微团聚体结合碳分别较坡顶高10﹪和18.7﹪.研究结果反映了土壤侵蚀以及耕作倾向于破坏水稳性大团聚体,其内部包裹的轻质、细颗粒物质易被地表水流迁移流失,加上下层土壤的稀释作用,导致侵蚀部位SOC减少.轻质活性碳组分在迁移和累积过程中易被微生物利用分解,沉积区土壤以IOC和微团聚体碳为主,形成一个惰性碳汇.     

湄公河流域土壤侵蚀空间特征及其优先治理区确定

湄公河流域拥有丰富的自然生态系统,为沿岸居民提供了食物、交通等众多方面支持,在东南亚地区具有极其重要的地位。土壤侵蚀是该流域主要环境问题,易引发土地退化和河流泥沙淤积。基于气候、土壤、遥感等区域数据产品,使用通用土壤流失方程(USLE,Universal Soil Loss Equation),对湄公河流域土壤侵蚀状况及空间分布特征进行探究,并通过联合信息熵方法,确定该流域土壤侵蚀的主导因素。结果表明,湄公河流域平均土壤侵蚀模数为1.98×10~3 t km~(-2) a~(-1),属轻度侵蚀;流域内近40%区域存在不同强度的土壤侵蚀,侵蚀较严重的地区主要包括11个子流域(M4—M7、M9、T4—T6、T8、T10、T20),是未来土壤侵蚀重点治理区域。土地利用类型、坡度和海拔是该流域土壤侵蚀的主导因素,其中灌丛和裸地/稀疏植被分别为强烈和极强烈侵蚀,土壤侵蚀模数与坡度的关系为随坡度的增加呈先增加后减小的趋势,和土壤侵蚀模数与海拔的关系相同。流域内剧烈程度侵蚀发生区主要特点为:土地利用类型为裸地/稀疏植被和灌木,海拔在500—2000 m,坡度在8—25°。基于优先级理论,对湄公河子流域的优先治理次序进行排序和划分等级,共分为4个等级,达到第一级的共3个子流域。通过以上研究分析以期能为湄公河流域今后的水土保持规划和管理工作提供一定的科学参考依据。     

土壤有机碳动态:风蚀效应

土壤风蚀是引起土壤退化最广泛的形式和原因之一。土壤风蚀对土壤碳动态的影响机制一方面是土壤风蚀引起土壤退化使土壤生产力下降,输入土壤的碳数量减少;另一方面是富含有机碳的细粒物质直接移出系统。风蚀土壤碳的去向包括:(1)就近沉积,(2)沉积于水渠和河流,输入水体;(3)以粉尘形式运移,在远离风蚀区的地域沉积;(4)氧化释放至大气。风蚀引起土壤碳的迁移和沉积不仅导致土壤有机碳在地域间的再分布,使土壤性状的空间异质性增加,也显著改变了土壤系统中碳矿化的生物学过程。土壤有机碳的保持可以促进团聚体的形成,使土壤物理稳定性增加,减缓风蚀。对易风蚀土地进行退耕还林还草、实行保护性耕作等措施可以有效增加土壤碳的固存。